1. Field of the Invention
The present invention relates to a device and a method for measuring the tread depth of at least one tire, in particular a motor vehicle tire.
2. Description of the Related Art
Various methods for manual or automatic tread depth measurement, mechanically or contactlessly measuring methods, and methods for measuring when the vehicle or tire is stationary or rolling are known for measuring the tread depth of tires.
Triangulation methods using laser scanners for tread depth measurement on a roller dynamometer are described in published German patent application document DE 197 05 047 A1 and European patent document. EP 1 394 503 B1, for example.
German patent document DE 43 16 984 describes a method for measuring the tread depth when the tire is stationary or is traveling over a measuring device. A triangulation sensor situated on a movable slide is moved along a line transverse to the rolling direction of the tire.
Published international patent application document WO 97/07380 A2 describes the use of a light section method, using one or multiple light sections for measuring as a tire travels over, in which the measuring device moves together with the vehicle.
German patent document DE 1 809 459 describes a light section method for measuring the tread depth as a tire travels over. The tread depth is measured along a single line in parallel to the rotational axis of the tire. The method is based essentially on the examination of shadows of the tread which are generated by an obliquely incident light source.
Published European patent application document EP 04 69 948 A1 likewise describes a device for automatically ascertaining the tread depth of motor vehicles in moving traffic. The measuring device is situated beneath the roadway surface. Instead of a light line transverse to the running direction of the tire, multiple light spots are measured, and the tread depth is deduced based on differences in light density of the imaged points. For increasing the accuracy, multiple measuring devices are situated in succession in the travel direction.
Published German patent application document DE 10 2009 016 498 A1 provides a method for ascertaining the tread depth of a vehicle tire, the tire being mounted on a vehicle, and in the method the tire is rolled over a measuring station or is stopped on same. The tread of the tire is optically scanned on at least one measuring line transverse to the rolling direction of the tire, a beam fan which emanates from a light source being reflected on the tire surface and a signal of the reflected beam fan being recorded by a sensor, and the signal of the reflected beam fan being evaluated with the aid of a triangulation method.
In published German patent application document DE 10 2006 062 447 A1, an area of the tire tread is likewise measured with the aid of a light section triangulation method while the tire rolls over a gap. The method provides for guiding an illumination line over the tread surface, transversely with respect to the rolling direction of the wheel, with the aid of a prism rotating at high speed. Due to the illumination line which moves in parallel, the entire section of the tire may be sequentially scanned with a high density while the tire surface situated on the gap is in the idle state relative to the measuring device.
European patent EP 0 469 948 B1, European patent EP 1 952 092 B1, and U.S. Pat. No. 7,578,180 B2 describe further variants of triangulation methods for measuring the tread depth while a tire travels over.
The object of the present invention is to provide an improved device and an improved method for measuring the tread depth of a wheel in particular of a motor vehicle, which are suitable for numerous tire widths, have high measuring accuracy, and are easy to operate and carry out.